Mobile phones are increasingly being used in conjunction with on-line payment service providers, such as PayPal, Inc. of San Jose, Calif. With the ever-increasing popularity of mobile devices such as smart phones and of Internet commerce, both consumers and sellers are using mobile devices to conduct financial transactions between parties, whether they are individuals or companies. For example, a consumer may launch a web browser on a mobile device to connect with a payment service provider over the Internet to request an on-line payment. The consumer may access his or her on-line account, provide payment information, and authorize the payment service provider to transfer funds from the consumer's account to a merchant's account. A confirmation message may then be sent to the consumer's or the merchant's mobile devices to complete the transaction. However, to facilitate payment transactions, and to enable payment transactions even when there is no Internet connectivity, it is desirable for a consumer's mobile device to communicate directly with a merchant's mobile device. For example, the consumer may use the mobile device to transmit information such as his or her account information and payment amount to the merchant's mobile device to authorize the payment. The merchant may later connect with the payment service provider for transmission of the information received from the consumer to complete the transaction.
While technologies such as near-field communication (NFC) and Quick Response (QR) codes have been proposed for secure communication of financial information between mobile devices, they suffer from various deficiencies. For example, NFC requires the installation of NFC-capable hardware and software on the mobile devices of both parties, thus increasing cost for users. QR code is a two-dimensional barcode (2D barcode), that may be displayed by a mobile device and scanned by a camera on another mobile device to communicate between mobile devices. However, a QR code is limited in the amount of data encoded therein, making its use impractical for the transmission of large amounts of data that may be encountered in a financial transaction. In addition, mobile devices may vary greatly in display and camera capabilities, making it difficult for a mobile device with a low resolution camera to accurately capture information encoded in a large QR code. Furthermore, accurate scanning of a large QR code may be time consuming and may require perfect focus or alignment of the scanning camera with the display, further limiting its ease of use. Accordingly, there is a need for a way to securely, easily, and economically communicate financial information between mobile devices to facilitate financial transactions.